1. Field of the Invention
The present invention relates to a new phenylazomethylene-cyclohexadienone derivative having an improved electron transferring capacity and an electrophotographic photoreceptor comprising the same. More particularly, the present invention relates to a new phenylazomethylene-cyclohexadienone derivative comprising an electron withdrawing group having a high electron affinity and an electrophotographic photoreceptor comprising the derivative singly or in combination with another compound having an electron transferring capacity as an electron transferring material of a photoconductive layer or undercoating layer.
2. Description of the Related Art
An electrophotographic photoreceptor is employed in electrophotographic image-forming apparatuses, such as facsimiles, copiers, laser beam printers, CRT printers, LED printers, liquid crystal printers, laser electrophotographs, and so on. Basically, in the electrophotographic image-forming apparatus, a photoconductive material is charged and exposed to an image-forming light source to form an electrostatic latent image. Then, the image is developed with toner (also referred to as ink) by applying a developing voltage, and after the toner image is transferred to a recording medium such as paper, or the like, the image is fixed thereon.
The electrophotographic photoreceptor comprises a photoconductive layer containing a charge generating material (CGM), a charge transferring material (CTM), and the like on a conductive substrate. Generally, the electrophotographic photoreceptor contains an additional functional layer; for example, an undercoating layer is formed between the conductive substrate and the photoconductive layer, or a protective layer is formed on the photoconductive layer.
The charge generating material of the photoconductive layer may be divided into two classes: an inorganic compound and an organic compound. The organic compound has generally been used as the charge generating material in recent years, considering environmental pollution, and the like. The photoreceptor in which this organic compound is used as the charge generating material is also referred to as an organic photoreceptor.
The photoconductive layer may have a single layer structure in which the charge generating material and the charge transferring material are dispersed together in a single layer, or a laminate (or multi-layer) structure in which the charge generating material and the charge transferring material are dispersed separately in a charge generating layer and a charge transferring layer, respectively. The photoconductive layer is classified into a (+) type and a (−) type, according to its potential to be generated upon charging. The single layer type photoreceptor has been studied mainly in the field of (+) type photoreceptor production, and the laminate type photoreceptor has been studied mainly in the field of (−) type photoreceptor production.
The photoconductive layer of the (+) type photoreceptor includes an electron transferring material, a binder resin and a charge generating material, and, in some cases, additionally includes a hole transferring material. Since the electron transferring capacity of the electron transferring material which is commonly used is 100 or more times smaller than the hole transferring capacity of the hole transferring material, the capacity of the photoreceptor is significantly influenced by the electron transferring capacity of the electron transferring material. Therefore, among materials included in the photoconductive layer of the (+) type photoreceptor, the selection of the electron transferring material is of significant importance.
The electron transferring capacity of the electron transferring material is significantly influenced by the electron affinity of the electron transferring material itself. Even when the electron transferring capacity of the electron transferring material is excellent, if the material alone cannot accept electrons effectively, it is common to use the material together with a material that aids the electron acceptance.
The conventional electron transferring material generally includes compounds having a naphthalenetetracarboxylic diimide structure, a dicyanofluorenone structure, a diphenoquinone structure, a phenylazomethylene-cyclohexadienone structure, or the like.
The compound having a naphthalenetetracarboxylic diimide structure represented by the following Formula 1 has an excellent electron transferring capacity, but lacks the capacity for accepting electrons from the charge generating material; therefore, another electron accepting material (or electron acceptor: EA) is needed. If the compound having the naphthalenetetracarboxylic diimide structure is used singly as an electron transferring material without the electron accepting material, the charging potential is seriously reduced, and the exposure potential is increased after repeated charging and exposure.

The compound having a dicyanofluorenone structure represented by the following Formula 2 has a poor electron transferring capacity, and therefore, even though the compound is used with an electron acceptor, the charging potential is seriously reduced, and the exposure potential is increased after repeated charging and exposure.

The compound having a diphenoquinone structure represented by the following Formula 3 is an electron transferring material that is commonly used and also serves as an electron accepting material. When the diphenoquinone compound is used singly or in combination with another compound having an electron transferring capacity, a stable charging potential and an exposure potential may be attained after repeated charging and exposure. However, when the diphenoquinone compound is used singly as an electron transferring material, the charging potential to be attained is stable but low, and thus, the image quality of the final printed image of the electrophotographic photoreceptor using the diphenoquinone compound is inferior.

The compound having the phenylazomethylene-cyclohexadienone structure represented by the following Formula 4 is disclosed in U.S. Pat. No. 6,472,514.

However, the electron transferring capacity of the compound disclosed in the above patent is ineffective, and the sensitivity and the remaining potential are substantial, indicating that the remaining potential is substantial after erasing after exposure, and therefore, the compound has a characteristic which is not suitable for an electrophotographic image forming apparatus.
Thus, an electron transferring material which itself has an effective electron accepting capacity without requiring another electron accepting material, and which also has an effective electron transferring capacity, is still needed.